Concatenation

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In computer programming, concatenation is the operation of joining two character strings end to end. For example, the strings "foo" and "bar" may be concatenated to give "foobar". In programming languages, string concatenation is a binary operation usually accomplished by putting a concatenation operator between two strings (operands).

For example, the following expression uses the "+" symbol as the concatenation operator:

print "Hello " + "World";

which produces the output:

   Hello World

Different languages

Main article: Comparison of programming languages (strings)

Different languages use different operators. Most languages use the "+" sign though several deviate from this norm.

Examples

   +       ;; ActionScript, BASIC, C++, C#, Java, JavaScript, Pascal, Python, Ruby, Windows PowerShell, SQL
   &       ;; Ada, AppleScript, VHDL, Visual Basic 
   .       ;; Perl (before version 6), PHP
   ||      ;; REXX, SQL

For a more detailed comparison, please see the concatenation comparison article.

Programming conventions

Assignment

Many languages, such as PHP and JavaScript have a variant of the assignment operator that allows concatenation and assignment to a variable in one statement.

For example, in PHP and Perl:

//Example 1 (concatenation operator ".")
$var = "Hello ";
$var = $var . "World";
 
//Example 2 (combined assignment and concatenation ".=")
$var = "Hello ";
$var .= "World";

Both examples produce the same result.

Interpolation

Some languages, (such as Perl, PHP, and most Unix shells), support variable interpolation as an alternative form of string concatenation.

For example, in Perl, the concatenation syntax:

my $stringVar;
$stringVar = "World"; 
print "Hello " . $stringVar;

can be substituted with the string literal syntax:

my $stringVar; 
$stringVar = "World";
print "Hello $stringVar";

since double quoted string literals in Perl indicate scalar variables with the sigil ($) character.

See also

• Formal language

External links

• Concatenation of languages (different from concatenation on strings)